In railway systems having long-stator linear motors, for example magnetic-levitation transport systems, the stator winding is arranged in the form of at least one rail-like phase along the travel path or track. The secondary part, cooperating with the long stator, thus with the primary part of a linear motor, and corresponding to the rotor of a conventional electric motor, is located on the vehicle, which moves along the travel path. There are railway systems with only one winding phase. However, the subject matter of the present invention is railway systems in which there are two winding phases arranged in parallel. For reasons of efficiency and of power requirements, the individual winding phases are usually subdivided into a plurality of stator sections (hereinafter referred to as sections) The individual sections are seperated from one another electrically and are supplied with current only when a vehicle travels over them. In order to permit continuous movement of the vehicle along the travel path, the current must be switched from a section no longer needed to the next following section of a winding phase. Because of the high voltages, this changeover of the sections must be effected at zero current. Switching over the current from one section to the section following next in the direction of travel is carried out in principle, such that initially the current of the presently active section is adjusted down, i.e., is reduced to zero. When the said section is in the currentless state, it is possible to change over to the next section and then the current is adjusted up again to its original value. Consequently, only a reduced thrust is available for driving the vehicle during the times of upward and downward adjustment. The sections are completely de-energized during the changeover or switch-actuating phase, so that no thrust at all is available. In order to avoid a complete loss of thrust, in the case of the railway systems under discussion, a second long stator or a second winding phase is present which is likewise subdivided into individual sections. The sections of the second winding phase are arranged offset relative to the sections of the first winding phase, so that the sectioning point between the successive sections of the one winding phase is overlapped by a section of the other respective winding phase. Various conventional section-changing methods are used for switching over the driving current.
In the so-called three-step method, a total of three section cable systems run along the travel path. The section cables of a drive region of the travel path are supplied with current from one substation (single infeed) or from two substations (double infeed). The sections of a winding phase which are needed in each case to drive the vehicle are continuously electrically connected to the section cables. Normally, i.e., when no section change is to be made, only two mutually opposite sections of the one and of the other winding phase or, viewed in the direction of travel, of the left and of the right winding phases, are active. Before a vehicle travels over a sectioning point between two successive sections, the section following the sectioning point is switched in. Thus, during the section change, the full electric power or full thrust is available. After the sectioning point has been traveled over, the section situated in advance of the sectioning point and no longer needed to drive the vehicle is switched off again. The disadvantage of this method resides principally in the high "hardware outlay". Three section cables and at least three converters must be provided in a substation. In another method, the so-called alternating-step method, which is described in, for example, from the article entitled "Energieversorgung des Langstatorantriebs" (POWER SUPPLY OF THE LONG-STATOR DRIVE) in the journal "etz" volume 108 (1987) issue 9, pages 378 to 381, only two section cables are present. Since a third section cable is lacking, but three sections are simultaneously traveled over during the section change, one of the three sections must always remain de-energized, which leads to a maximum thrust dip of 100% of the winding phase affected. The cause of this thrust dip is that during the section change described above, the sections to be changed over are completely de-energized during the changeover phase, and only the section of the other winding phase which overlaps the sectioning point is active. This has a negative effect on traveling comfort in the form of jerking, and causes system fluctuations in the supply system of the substations.
It is an object of the invention to reduce the thrust dip when working with an alternating-step method.
The starting point in achieving the set objective was double-infeed railway systems. In the case of double infeeding, the section cable of a drive region is supplied with power from two substations which are arranged at the ends of the section cable. A converter is present in each substation for each section cable. The basic idea of the present invention consists in splitting a double-infeed section cable electrically into two subphases during a section change, the one subphase being supplied with power from one substation and the other subphase being supplied from the other substation in single infeed. At the time of the section change, there is then a total of three voltage sources available for the three sections simultaneously being traveled over during a section change. Owing to the splitting up of the one cable section, the two substations deliver only half the electric power to the two sections to be changed over (compared to the full power in the case of double infeeding), with the result that in total only 150% of the electric power or of the maximum possible thrust of 200% is available.